Valve For A Vibration Damper, Vibration Damper, And Motor Vehicle

ABSTRACT

A valve for a vibration damper having a valve housing and a valve slide movable in the valve housing for at least partially closing at least one flow path of a fluid flowing through the valve. The valve has an input side and an output side. The pressure impingement surfaces of the valve slide for an opening pressure and for a closing pressure are substantially equal, and the valve slide has a constriction via which a pressure difference between opening pressure and closing pressure can be generated. At least one channel connects the interior space of the valve slide to the exterior space of the valve slide.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a U.S. national stage of application No. PCT/EP2015/050222,filed on Jan. 8, 2015. Priority is claimed on German Application No.DE102014202440.4, filed Feb. 11, 2014, the content of which isincorporated here by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to a valve for a vibration damper comprising avalve housing and a valve slide movable in the valve housing for atleast partially closing at least one flow path of a fluid flowingthrough the valve, the valve having an input side and an output side.

2. Description of the Prior Art

It is known to use valves in vibration dampers. In two-tube vibrationdampers, there is usually a base valve at a bottom of the workingcylinder. Further, the piston can have a piston valve. In this case, thevalves are compression valves.

It is further known, e.g., from DE 34 34 877 A1, to provide two-tubedampers with an adjustable damping force in that a damping forcegenerating device outside of the two-tube damper is fluidicallyconnected to the interior of the two-tube damper. The resistance to thefluid can be adjusted at this damping valve to control the damping forceof the vibration damper.

To produce damping valves of this type more economically, it isnecessary to limit the volume flow through the damping valve. Of course,flow valves for influencing the flow of a fluid are already known. Inparticular, there are two-way flow control valves, three-way flowcontrol valves, or flow-dividing valves. Known flow valves cannot beutilized for the targeted application in a vibration damper because theyare either electrically operated or, by reason of their manner ofoperation, cannot be controlled purely as a function of volume flow.

A vibration damper with adjustable damping force in which an additionaldamping valve is arranged upstream of an adjustable damping valve isknown from DE 102004054474 B3. In this way, suddenly occurring maximumpressures, for example when driving over a bump, can be contained andkept away from the adjustable damping valve.

SUMMARY OF THE INVENTION

It is an object of the present application to provide a valve that canbe operated passively, i.e., mechanically or hydraulically, andcontrolled substantially depending on volume flow and, therefore,independent of pressure so that a device that is connected to thevibration damper such as a damping valve can be operated with a maximumvolume flow.

It is provided that the pressure impingement areas of the valve slideare substantially the same size for an opening pressure and for aclosing pressure, and the valve slide has a constriction via which apressure difference between opening pressure and closing pressure can begenerated, and at least one channel connects the interior space of thevalve slide to the exterior space of the valve slide.

In this regard, the opening pressure moves the valve slide out of thenormal position in the direction of the overload position, while theclosing pressure propels the valve slide in the opposite direction.Accordingly, the opening pressure impinges on surfaces that face theinput side and the closing pressure impinges on surfaces that face theoutput side. Input side and output side refer to the regions inside andoutside of the valve slide which are above and below the constrictionor, when installed horizontally, lateral to the constriction. Thoseareas that are arranged facing the piston as viewed from theconstriction after the valve has been installed in a vibration damperare located on the input side and those areas that are correspondinglyarranged remote of the piston are located on the output side. In thisregard, it is assumed that the vibration damper is in rebound and thefluid of the vibration damper accordingly has a definite flow direction.

The pressure impingement areas are those cross-sectional areasdiametrical to the constriction as projection on the cross-sectionalarea in direction of the longitudinal axis or movement direction of thevalve slide. The pressure impingement areas must be substantially equalin size, i.e., the projected surfaces contain the same, or only slightlydifferent, surface area. In particular, this does not mean that thevalve slide must be constructed symmetrically above and below or lateralto the constriction; rather, the inner walls can be shaped differentlyon the input side and output side. Further, the pressure impingementareas can be formed of a plurality of parts in each instance. Also, noother kinds of symmetries are necessary in axial direction; the valveslide is preferably formed so as to be rotationally symmetrical. Auniform pressure distribution and pressure impingement can be achievedin this way.

Further, it is preferably provided that the valve slide has a basicallyhollow-cylindrical shape. By this is meant that the valve slideseparates an interior space from an exterior space. It is not necessarythat the inner wall or walls or the outer wall have any particularshape. In particular, the walls need not be “smooth”; they can also bestepped. However, it is preferably provided that there is a continuouscross-sectional reduction toward the constriction, specifically fromboth the input side and output side, so as not to cause flow separation.

The pressure impingement areas preferably occupy less than one half andmore than one fourth of the total cross-sectional area of the valveslide. In a particularly preferred manner, the pressure impingementareas occupy more than one third of the total cross-sectional area ofthe valve slide and, more preferably, more than 40 percent of the totalcross-sectional area of the valve slide.

The pressure ratios under fluid flow are as follows: on the input side,the opening pressure p1 is present on the entire surface. The diameterdecreases toward the constriction, which is why the flow velocityincreases toward the constriction, while the pressure decreases. Afterpassing the constriction, however, the flow velocity of the fluiddecreases again and the pressure increases until the other end of thevalve slide is reached. Pressure that is lower than the opening pressurep1 is tapped through the channel so that the exterior space around thevalve slide also has this pressure level.

The channel can preferably connect the interior space of the valve slideto an annular space around the valve slide, particularly an annularspace accommodating a spring. The annular space is enclosed by the valveslide on the one hand and by the valve housing on the other hand.Accordingly, the pressure-impinged opening surfaces and closing surfacesare the same size.

In a particularly advantageous manner, the at least one channel can bearranged in the region of the constriction. In this case, the pressureat the constriction and, therefore, the lowest pressure within the valveslide, is tapped.

In a particularly preferable manner, the valve slide has at the inputside a circumferential projection that guides the valve slide in thevalve housing and limits an annular space around the valve slide on oneside. In this case, the opening cross section of the interior space ofthe valve slide is preferably larger on the input side than on theoutput side. This difference in cross section is occupied substantiallyby the circumferential projection. Accordingly, the pressure impingementarea for the closing pressure is divided in two. Different pressuresthen also act on the different pressure impingement areas. Bothpressures p2 and p6, which act as closing pressure, are smaller than theopening pressure p1 because the latter is present at the location of thelargest cross section and, therefore, at the location of the greatestpressure as well as the lowest velocity.

In this way, the pressure difference generated by the constrictionbetween the opening pressure and closing pressure can be increased andthe stability of the opening process and closing process can beimproved.

The cross-sectional surface of the channel or channels is preferablylarger, particularly at least five times larger, preferably at least tentimes larger, than the leakage area located between the circumferentialprojection of the valve slide and the valve housing. The leakage areacannot be avoided; a slight radial play is required around an axial. Thedifference in surface area between the channels and the leakage ensuresthat the tapped internal pressure of the valve slide, particularly thepressure at the constriction and not an undefined pressure, is presentin the annular space.

Accordingly, under fluid flow the closing pressure, i.e., the pressuresthat move the valve slide in the normal position is always less than theopening pressure, but the pressure impingement areas are identical.Therefore, the valve is dependent on the volume flow.

The pressure difference that can be generated between opening pressureand closing pressure through the constriction first takes place, ofcourse, when a fluid is flowing. Without movement of the fluid, there isno pressure difference between the input side and output side of thevalve.

The valve slide preferably has one individual constriction forgenerating a pressure difference between opening pressure and closingpressure. Therefore, this constriction is preferably arranged in thecentral region of the valve slide. Preferably, the constriction isprovided between a top fourth and a bottom fourth of the valve slide.

In an advantageous manner, the valve slide can be preloaded by an energystorage, particularly a spring. The valve slide of the valve which iscontrolled as a function of volume flow is displaceable in the valvehousing. The valve slide must have a preferred position so that thevalve slide has a fixed initial position, i.e., the valve slide isalways to be found in a definite position when put into operation. Thispreferred position can be predefined by the energy storage. The forceexerted by the energy storage should be at least sufficient to fix thevalve slide in the preferred position against friction and, depending onthe installed position, also against its own weight force. Thepreloading force of the energy storage can also be used to affect howlarge the volume flow must be to move the valve slide out of the normaloperating position. The energy storage is preferably supported againstthe valve housing. The valve housing can be formed of one, two or moreparts. The spring is preloaded between the valve slide and that part ofthe valve housing that is remote of the preferred position insofar as acompression spring is concerned or on the side of the preferred positionwhen a tension spring is used. Of course, these considerations alsoapply to other types of energy storages. What is crucial is whether theenergy storage exerts a tensioning force or a compressing force.

The preferred position of the valve slide is the normal operatingposition of the valve. Since the opening pressure and the closingpressure on the pressure-impinged areas substantially compensate for oneanother in normal operation, i.e., in the normal operating position ofthe valve slide, the valve slide remains in the preferred position untilthe volume flow through the valve slide exceeds a threshold value sothat the differential pressure between the input side and the outputside, and possibly between the input side and annular space, pushes thevalve slide out of the normal operating position and moves it indirection of the overload position. In principle, the valve slide isselectively displaceable between the normal operating position and theoverload position.

The constriction is advantageously formed as a circular narrowing.Accordingly, the inner diameter of the valve slide narrows at a certainaxial height, this reduced inner diameter comprising a predefined,contiguous portion. In principle, the narrowing can be formed in astepped manner, but the valve slide is preferably formed so as toproceed to termination in a conical manner toward the constriction onthe input side. Following the constriction, the inner diameterpreferably likewise increases uniformly.

It should be mentioned that the constriction need not be formed as anarrowing. For example, the constriction can also be realized in that aplate with bores is located in the valve slide. However, this varianthas the disadvantage that the volume flow is impeded no matter what thevolume in the flow, and production is more elaborate compared to thepreviously described embodiment.

The valve slide can preferably have a larger flow area at the outputside in a first operating position, particularly a normal operatingposition, and a smaller flow area in a second operating position,particularly an overload position. In this way, the flow resistance ofthe fluid can be controlled. With a larger flow area, the fluidencounters less resistance and can accordingly flow unimpeded.Decreasing the flow area in the overload position increases the flowresistance; further, the volume flow is limited to a maximum value.

The walls of the valve slide on the output side can preferably have atleast one recess. This recess which goes through the entire wall ensuresthat even in the overload position an opening through which the fluidcan flow always remains open. In this way, at least one volume flow,which is set by the size of the recess, is always admitted to thedamping valve. The recess can be provided in the manner of a notch orslit at the underside of the wall of the valve slide, but can also beinserted in the wall of the valve slide in the manner of a window sothat the valve slide is closed at the lower edge. The definitiveposition of the recess depends inter alia on the flow path of the fluid.

In an advantageous manner, the valve slide has at least two recesses,and these recesses are arranged symmetrically. With a symmetricalarrangement of the recesses, the valve slide—and therefore the valve—ismore balanced with respect to force compared to an asymmetricalarrangement, which is why a symmetrical arrangement is preferred.Depending on the size and arrangement of the recesses, a quantity of sixto eight recesses is particularly advantageous.

The valve slide can preferably have at least one stop that limits therelative movement with respect to the valve housing. It is thenpossible, regardless of the presence of recesses at the output side, toalways leave an opening for the fluid in the overload position on theoutput side. The opening cross section on the output side can also bemaintained in its entirety regardless of the position of the valveslide.

The valve housing is preferably supported on at least two feet thatextend from the outer edge of the valve housing to the center of thevalve housing. Because the feet do not reach to the inner edge of thehousing, a radial free space always remains around the valve slide sothat recesses at the output side of the valve slide never overlap withthe feet, which could in turn inhibit the flow of fluid. Preferably, thecenter of the valve housing is offset somewhat toward the radially innerside compared to the outer edge of the top housing portion of the valvehousing. Accordingly, the same area that is also supported on the valvehousing above the valve housing remains accessible for the fluid belowthe valve housing. In this way, in addition to the radial free spacewith respect to the recesses of the valve slide, a pressure balance ofthe valve housing can be achieved.

Preferably, a main flow path, which can be closed by the valve slide,can be fluidically connected as flow path with the output side of thevalve; that is, the main flow path is considered to be that path thatfollows the valve and valve slide on the output side. Therefore, theabove-described preferred position for the valve slide, and, therefore,also the normal operating position, is a positioning of the valve slideremote of the output side; accordingly, an energy storage for preloadingthe valve slide is to be supported between an input-side portion of thevalve slide and an output-side portion of the valve housing insofar asthe energy storage is compressive. In case of a tensile energy storagesuch as a tension spring, however, this energy storage would be arrangedbetween an output-side portion of the valve slide and an output-sideportion of the valve housing.

In an advantageous manner, a bypass path, which can be closed by thevalve slide, can be fluidically connected as a flow path in the inputside of the valve. Instead of a bypass path, a pressure limiting valve,for example, could also be provided in the piston so that the fluid isconducted through the piston when a valve is in the overload positionand, therefore, as pressure rises. However, a pressure limiting valve inthe piston assumes that a higher pressure can be built up. Since theexisting pressure and the volume flow are linked, the value that isaccordingly predetermined through the damping force generating devicevia the volume flow is so small that the pressure limiting valve mustalready operate in a pressure range in which it should actually not yetbe operative. The bypass path accordingly offers the advantage that onthe one hand the piston can be constructed in a simplified manner and onthe other hand it is accordingly possible to divert merely the surplusportion of the volume flow.

In particular, the valve slide can also be displaceable in such a waythat it merely opens and closes the bypass path depending on the volumeflow flowing through the valve slide and leaves the main flow pathunchanged. For this purpose, the valve slide in the overload positioncan be supported at a stop on the output side, and the flow area of themain flow path is not reduced or is not substantially reduced. This isalso achieved when the valve slide is supported by feet on the bottom ofthe main flow path insofar as the cross section of the latter reducesthe flow area only negligibly.

Preferably, the valve slide has at least one guide. The guide can beconstructed, for example, as a kind of outer ring on the outer side ofthe valve slide. The guide is preferably positioned on the input side ofthe valve slide. In this case, the valve slide has one individual guide.Of course, it is also possible to provide a plurality of projections asa guide, for example. A space is to be provided under the guide, sincethe guide is raised and lowered when the valve slide moves from thenormal operating position into the overload position and back again anda corresponding movement space is to be provided for this purpose. Thisspace can also be adjoined, for example, by the space for accommodatingthe energy storage provided the normal operating position lies towardthe input side and the energy storage is a compression spring.

Advantageously, a pressure limiting valve can be arranged in the bypasspath. This pressure limiting valve is preferably constructed as a checkvalve preloaded in the closing direction. Accordingly, the bypass pathalso has a certain flow resistance so that not all of the fluid volumeflows off via the bypass path when the valve slide moves into theoverload position and only a vanishingly small portion still remains onthe main flow path. Rather, a constant, maximum required volume ormaximum volume flow continues to flow through the recesses at the outputside of the valve slide. In this embodiment, the valve is a seat valvewith downstream valve in the bypass path.

In addition, one aspect of the invention is directed to a vibrationdamper for a motor vehicle that has a valve such as that described. Allof the embodiments of the valve can also be transferred in acorresponding manner to a vibration damper comprising a correspondingvalve.

Preferably, the vibration damper can have three tube elements arrangedone inside the other, and a displaceable piston is arranged in theinnermost tube element, the valve is arranged in or at the innermosttube element, and the center tube element separates a main flow pathfrom a bypass path, which main flow path and bypass path are fluidicallyconnected to the interior of the innermost tube element. As wasexplained in the beginning, the valve, which has been extensivelydescribed above, is provided for a vibration damper, but the specificconstruction of this vibration damper does not depend on theconstruction of the valve. The constructional composition of thevibration damper is arrived at in that the vibration damper comprisesthree tube elements in coaxial arrangement with respect to one another.The construction is similar to a two-tube damper with intermediate tube,but there is no gas in the exterior space of the present vibrationdamper so that this space does not represent a compensation space.Further, the central volume and outer volume are preferably connected tothe working space, i.e., the space in the inner tube element, such thatthe fluid flowing in the main flow path and in the bypass path can bereturned again to the working space, specifically above the piston whenthe vibration damper is excited in compressive direction.

The compensation space can be arranged lateral to or below the tubeelements, but can also be part of the three tube elements. Inparticular, the compensation space can be arranged on the side of thevalve remote of the piston.

A damping force generating device can preferably be arranged in the mainflow path. As was described above, this damping force generating devicemust be protected against excessively large volume flows, which isachieved by means of the valve.

One aspect of the invention is directed to a motor vehicle comprising avibration damper such as that described.

Further embodiments, details and features are indicated in theembodiment examples and figures described in the following. In thedrawings:

FIG. 1 is a portion of a vibration damper in longitudinal section;

FIG. 2 is a valve slide;

FIG. 3 is a pressure limiting valve;

FIG. 4 is a guide portion in cross section;

FIG. 5 is a diagram showing the dimensions of a valve slide;

FIG. 6 is a hydraulic circuit diagram; and

FIG. 7 is a valve as slide valve.

FIG. 1 shows a portion of a vibration damper 1 with an inner tubeelement 2, an outer tube element 3, a center tube element 4 arrangedbetween the inner tube element 2 and outer tube element 3, and a valve5. A bypass path 6 is located between the inner tube element 2 and thecenter tube element 4, and a main flow path 7 is located between thecenter tube element 4 and the outer tube element 3. A damping forcegenerating device, e.g., a damper valve 8, which is to be protectedagainst excessively large volume flows, is located in the main flow path7 or in the fluidic connection to the main flow path 7. A piston 9 thateither works as a simple displacer or a compression valve that opensunder very high pressures is provided in the inner tube element 2. Thevalve 5 substantially comprises a valve slide 10, a valve housing 12comprising housing parts 14 and 16, a spring 18, a pressure limitingvalve 20, and feet 22. There are two channels 21 between the interiorspace 23 of the valve slide 10 and the exterior space 25 thereof.

FIG. 2 shows the valve slide 10 in more detail. The valve slide 10 hasan input side 24 on the piston side and an output side 26 remote of thepiston. The terms “piston side” and “remote of the piston” refer to thevalve 5 in installed state in a vibration damper 1. In the following,the valve slide will be described from the input side 24 toward theoutput side 26. The top of the valve slide 10 is formed by surface 28.Surface 28 is located on a narrow annular projection that terminateswith the stop 59 toward the outer side. Accordingly, surface 28 is thevalve surface of valve 5 constructed as a seat valve and locatedopposite the valve seat surface 29. Toward the inside, surfaces 30 and32 form a conically narrowing funnel that opens into the side surface34. Surface 38 follows the side surface 34 extending parallel to theouter side 36. Surface 38 has the same slope or a similar slope relativeto side surface 34 as surface 32; that is, the inner diameter widenstoward the constriction 40 on the output side 26 to the extent that itdecreases on the input side 24 in front of the constriction 40. Thiscontinuous narrowing and widening is intended to prevent flowseparations. What is important here is not that the pitch is the same,but that the pitch is constant and there is no excessive opening angle.

Owing to the shape of the valve slide 10, the exterior space 25 includesa part of the space radially outside of the valve slide 10, while theinput side 24 and the output side 26 are not added on. In any case, theinterior space 23 contacts the input side 24 and output side 26, whichis why there is no reason for a channel connecting these spaces.

There are two radially extending channels 21 in the region of theconstriction 40. These channels 21 are configured as through-openingsand connect the interior space 23 of the valve slide to the exteriorspace 25, in this case, the space that receives the spring 18. Insteadof two channels, one or three or more channels can also be provided.They are preferably distributed symmetrically in circumferentialdirection. This quantity and symmetry of the channels is not limited tothe embodiment form described, but rather applies in general. Thechannels need not lead perpendicularly through the wall of the valveslide, although that is a preferred configuration.

FIG. 2 shows the following characteristics for pressure-balancing thevalve 5.

The inner edge 46 on the input side 24 of the valve slide 10 lies in a(longitudinal) plane with the outer side 48. This is the same plane inwhich the projection 54 terminates outwardly. Accordingly, the surfacesimpinged by the opening pressure p1 and the closing pressure p2 and p6are the same size (see FIG. 5). The pressure impingement areas can bedetermined through a projection of the cross section on a planeperpendicular to the longitudinal axis or movement direction of thevalve slide 10. In other words, as long as the inner diameter and outerdiameter of the pressure impingement areas are equal, they are impingedequally with the same opening pressure p1 and closing pressure p2 and p6regardless of the slope of surfaces 30, 32 and 38. In this embodiment ofthe valve slide 10, however, a pressure difference is produced by thevolume flow flowing through the valve slide 10. This results in thefollowing manner:

The resulting force on the slide F equals the difference between theopening pressure p1 and the closing pressure p2 and p6 which aremultiplied, respectively, by the pressure-impinged area. The pressureimpingement area a1 for the opening pressure p1 can be determined by thediameter of the valve slide 10 on one side at the height of surface 28at inner edge 46 (diameter dsf) and at the height of side surface 34(diameter dsi)—see also FIG. 5. In other words, the diameters at thevalve surface, in this case the inner diameter of surface 28, and at theconstriction 40 are to be used to calculate area a1. Using simplegeometric circle calculations, area a1 is accordingly equal to thedifference between a larger-area circle at the height of surface 28 anda smaller circle at the height of side surface 34. Basically equaldiameters are used in calculating pressure impingement area a2 ofclosing pressure p2 so that areas a1 and a2 are equal. This results asfollows: to calculate the pressure-impinged area a2 during closingpressure p2 and p6, diameter dsi at constriction 40 is used on the onehand as with opening pressure p1, and the diameter defined by the outerside 48 is used on the other hand. The pressure-impinged area a2 for theclosing pressure is accordingly given by the pressure on surface 38 andon surfaces 50 and 52. Accordingly, area a2 is comprised of areas a21and a22. These annular areas transition smoothly one into the otherbecause they have outer side 36 as transition point. Like surface 38,surface 52 contributes to area a21. The reason why the diameter to beused is determined not by the inner edge 57 of surface 52, which wouldalso be possible in principle, but by the outer edge 55 of surface 52 isdue to the fact that surface 52 is also acted upon by fluid and,therefore, by pressure. Accordingly, however, diameters that are exactlyequal to those used for calculating pressure impingement area a1 enterinto the calculation of pressure impingement area a2. Therefore, apressure difference results only by reason of the volume flow of themoving fluid, and this pressure difference depends on the diameter orcross-sectional area a4 of the constriction 40.

Constriction 40 causes a pressure difference in a twofold manner. On theone hand, it causes a pressure drop, and the pressure p5 measured thereas pressure p6 on surface 50 impinges on a portion of the pressureimpingement area a2. Further, the inner diameter of the valve slide 10no longer widens to the initial size and, for this reason, pressure p2is always less than opening pressure p1. In addition, a portion of thekinetic energy of the flowing fluid dissipates to heat owing toconstriction 40 so that there is also a pressure drop between theopening pressure p1 and pressure p2. These three operative mechanismsfor generating a pressure difference between the opening pressure p1 andthe closing pressures p2 and p6 are advantageously cumulative.

There is also always a difference between the opening pressure p1 andclosing pressure p6 during slight heat dissipation. Even if it isassumed that the closing pressure p2 and opening pressure p1, which acton area a21 and the corresponding portion of area a1 are also equalunder fluid flow, there still remains the difference between pressuresp6 and p1 on area a22 and the corresponding portion of a1. Thisdifference is sufficient by itself to control the valve 5 purely as afunction of volume flow.

The diameter dka of channels 21 is dimensioned such that the pressure p6acting on surface 50 corresponds completely or at least substantially topressure p5 at constriction 40. To this end, the cross-sectional area ofall of the channels 21 must be a multiple of the leakage area betweensurface 48 and housing part 16. In particular, the cross-sectional areaof channels 21 is five times, preferably ten times, and particularlypreferably fifteen times, as large as the leakage area of the exteriorspace 25 around the valve slide 10. In particular, the diameter dka ofchannels 21 is between one and five millimeters, preferably between twoand four millimeters, and particularly preferably between 2.5 and threemillimeters. This applies to all of the embodiments independent fromother features particularly of the valve slide, valve housing and valve.

On the output side 26, the valve slide 10 has a plurality of recesses53. These recesses 53 can be passages from the underside of the valveslide 10, as is shown, but can also be arranged as a type of window atsome distance from the underside so that the valve slide 10 is closed onthe underside. Of course, the recesses 53 extend through the wall of thevalve slide so that there is always a minimum volume flow even in theoverload position. Valve slide 10 is arranged in the normal operatingposition in FIG. 1 and in FIG. 2. This preferred position results fromthe preloading by spring 18. In the embodiment form according to FIGS. 1and 2, the normal operating position is characterized in that the valvesurface, i.e., surface 28, is pressed against the opposite surface,namely, the valve seat surface 29. The bypass path 6 is closed in thisposition.

On the input side 24, the valve slide 10 has an annular projection 54.Below this, when the spring 18 is not arranged below the projection 54,there is also always a certain hollow space resulting from the lift pathof the projection 54 during the movement of the valve slide 10. When thespring 18 is arranged between projection 54 and valve housing 12, thishollow space is larger on the outer side 36 of the valve slide 10.

FIG. 3 shows the pressure limiting valve 20 according to FIG. 1 indetail. The pressure limiting valve 20 is formed as a check valvepreloaded in closing direction. It comprises at least one elasticallydeformable disk 58, two rings 60 and 62, and a disk package 64. The ring60 is supported on the elastically deformable disk 58, and the diskpackage 64 is fixed between rings 60 and 62. The deviation point 66 ofthe ring 60 is located such that an opening pressure of several bar,preferably between 2 bar and 15 bar, must be overcome before the fluidflows through the bypass path 6. This prevents the pressure fromdropping abruptly at the damping valve 8 in the main flow path 7 whenthe bypass path 6 opens.

An oil reservoir 68 is provided below the elastically deformable disk58.

FIG. 4 shows the valve slide 10 in a top view. Following surface 28 fromthe outer side to the inner side are surfaces 30 and 32, whichincreasingly reduce the inner diameter of the valve slide 10 until itreaches its smallest value at the constriction 40. Diameters d_(da),d_(sf) and d_(si) are shown for purposes of orientation and aredescribed more fully referring to FIG. 5.

To illustrate the dimensions mentioned with reference to FIG. 2, FIG. 5shows these dimensions separately from FIG. 2 for the sake of clarity.The indicated diameters have reference characters starting with a “d”,while area designations are denoted by “a”. Of course, the surfacesextending perpendicular to the drawing plane are not depicted as such.The following dimensions are given proceeding from the input side 24:

The vibration damper 1 in which the valve 5 can be installed presents aninlet diameter dzu. The next diameter shown is the inner diameter dsfalong the inner edge of surface 28. Both pressure impingement surface a1and pressure impingement surface a2 can be calculated via this innerdiameter dsf depending on inner diameter dsi. Further, the innerdiameter dsi predetermines the cross-sectional area a4 of theconstriction 40:

${a\; 1} = {{\pi \cdot \left( \frac{dsf}{2} \right)^{2}} - {\pi \cdot \left( \frac{dsi}{2} \right)^{2}}}$${a\; 2} = {{\pi \cdot \left( \frac{dda}{2} \right)^{2}} - {\pi \cdot \left( \frac{dsi}{2} \right)^{2}}}$${a\; 4} = {\pi \cdot \left( \frac{dsi}{2} \right)^{2}}$

It should be noted that the first part of the formulas for calculatinga1 and a2 correspond because the diameter dsf along the inner edge ofsurface 28 for calculating a1 and the diameter dda at surface 50 forcalculating a2 are equal by reason of the structural design of the valveslide 10.

The pressure impingement area a2 is formed of partial areas a21 and a22.Using diameter d_(fr):

${a\; 21} = {{\pi \cdot \left( \frac{dfr}{2} \right)^{2}} - {\pi \cdot \left( \frac{dsi}{2} \right)^{2}}}$and${a\; 22} = {{\pi \cdot \left( \frac{dda}{2} \right)^{2}} - {\pi \cdot \left( \frac{dfr}{2} \right)^{2}}}$

As can easily be seen, pressure impingement areas a21 and a22 sum to a2.Analogously, pressure impingement area a1 can be divided conceptuallyinto corresponding pressure impingement areas all and a12. The formulascorrespond to those for a21 and a22. A pressure difference betweenopening pressure and closing pressure can then also be generated in themanner described in the following.

Closing pressure p6 acts on pressure impingement area a22, and closingpressure p1 acts on pressure impingement area a12. With flowing fluid,the pressure in the valve slide at the constriction 40 is lowest; thefaster the fluid flows, the greater the pressure difference. This isknown as the Venturi effect and can be calculated using Bernoulli'sequation. When a threshold value is exceeded, the preloading force ofspring 18 is overcome and the bypass path 6 is opened.

In addition, a pressure difference occurs between the input side 24 andoutput side 26 through the constriction 40. This difference betweenpressures p1 and p2 acts on pressure impingement areas a11 and a21 andincreases the force acting on the valve slide.

FIG. 5 further shows the outer diameter dda, the distance hb of surface28 from valve seat surface 29, and the distance hd from the surface 52to the bottom of the main flow path 7. Distance hb represents the heightof the opening of the bypass path 6 and distance hd shows the height ofthe outlet area a31.

Outlet area a31 is an annular area which is the product of acircumference and a height. The circumference depends on the diameterdik defined by the inner edge 55; the height is, as was described above,the distance hd from surface 52 to the bottom of the main flow path 7.In the overload position, distance hd is equal to zero, and it reachesits maximum value in the normal operating position. Accordingly, theoutlet area a31 can also vary from zero to a maximum value:

${a\; 31} = {2 \cdot \pi \cdot \frac{dik}{2} \cdot {{hd}.}}$

Outlet area a32 designates the area defined by all of the recesses 53.Outlet area a32 is that area in the main flow path 7 that is always openfor producing a minimum flow. The total cross-sectional area a3 is equalto the sum of areas a31 and a32.

The outlet area a5 is also an annular area. The circumference which musttherefore be determined is equal to the inner diameter dsf and theheight is equal to distance hb:

${a\; 5} = {2 \cdot \pi \cdot \frac{dsf}{2} \cdot {{hb}.}}$

Like distance hd, distance hb can vary from zero to a maximum value and,of course, the value of distance hd can be smaller if distance hb islarger.

hb+hd=const.

Of course, this only applies when the flow area at the output side 26can be varied. On the other hand, in an embodiment in which only thebypass path 6 is opened and closed and the flow area of the main flowpath 7 remains constant, the total cross-sectional area a3 is constant,in which case it need not be formed of a plurality of areas.

Outer diameter dda is the outer diameter of the projection 54 withoutthe stop 59. This diameter is also shown in FIG. 4.

The cross-sectional area a6 of the pressure limiting valve 20 is shownin FIG. 3 but not in FIG. 5. Like outlet areas a31 and a5,cross-sectional area a6 is an annular area. The height corresponds tothe height of the gap opened by the disk package 64, which height canaccordingly be varied between zero and a maximum value. Thecircumference for calculating cross-sectional area a6 is defined bysupport point 67. Support point 67 is, of course, only a point in crosssection; in actuality, it is a support circle.

FIG. 6 shows a hydraulic schematic diagram of the valve according toFIG. 1. The dimensions shown in the drawing correspond to the dimensionsthat were used in the previous description of the figures. Owing to apiston movement, a total volume flow Qges is present on the input side24 of valve 5. The constriction 40 with an area a4 lies between theopening pressure p1 and the closing pressure p2. Area a4 of constriction40 is evident from inner diameter dsi. Following the constriction 40 inthe flow path is total cross-sectional area a3 given by outlet area a31and outlet area a32 in the normal operating position and only by outletarea a32 in the overload position. In the overload position, outlet areaa31 is closed by the valve slide 10. Instead, outlet area a5, whichconnects the input side 24 and the bypass path 6, is open. Accordingly,at the output side 26 the valve slide 10 has a larger flow area in afirst operating position, namely, the normal operating position, and asmaller flow area in a second operating position, namely, the overloadposition.

It further follows from FIG. 6 that the total volume flow Qges comprisespartial volume flows Q1 and Q2. Q1 is the volume flow flowing in thebypass path 6 and Q2 is the volume flow flowing in the main flow path 7.In the normal operating position, total volume flow Qges and partialvolume flow Q2 are identical, since the bypass path 6 is closed.Further, a compensation space 70 not shown in FIGS. 1 to 5 can be seenin FIG. 6. The compensation space 70 fluidically communicates with theinterior volume of the inner tube element 2. This receives the fluidvolume displaced by the piston rod. Oil is preferably used as fluid;however, the valve 5 may be operated with any incompressible fluid inprinciple.

The action of channels 21 is shown through the connection between theconstriction 40 with connection line a5-a31: the channels split theclosing pressure p6 and accordingly increase the pressure differencebetween opening pressure p1 and pressures p2 and p6 acting in closingdirection.

FIG. 7 shows a further embodiment form of valve 5 as slide valve, whileFIGS. 1, 2 and 5 show a seat valve. Only slight modifications are neededto get from the construction of the valve 5 as seat valve to a slidevalve. On the input side, the stop 59 must be removed from the valveslide 10 so that the outer surface 48 fully extends to surface 28.Further, housing part 14 must be reconfigured such that the valve slide10 cannot seat but rather can close the bypass path 6 by sliding pastit. All further arrangements correspond to the previous description.

Thus, while there have shown and described and pointed out fundamentalnovel features of the invention as applied to a preferred embodimentthereof, it will be understood that various omissions and substitutionsand changes in the form and details of the devices illustrated, and intheir operation, may be made by those skilled in the art withoutdeparting from the spirit of the invention. For example, it is expresslyintended that all combinations of those elements and/or method stepswhich perform substantially the same function in substantially the sameway to achieve the same results are within the scope of the invention.Moreover, it should be recognized that structures and/or elements and/ormethod steps shown and/or described in connection with any disclosedform or embodiment of the invention may be incorporated in any otherdisclosed or described or suggested form or embodiment as a generalmatter of design choice. It is the intention, therefore, to be limitedonly as indicated by the scope of the claims appended hereto.

1.-16. (canceled)
 17. A valve having for a vibration damper comprising:a valve housing; an input side of the valve; an output side of thevalve; a valve slide movable in the valve housing configured to at leastpartially close at least one flow path of a fluid flowing through thevalve; a first pressure impingement surface of the valve slide for anopening pressure; a second pressure impingement surface of the valveslide for a closing pressure, the first pressure impingement surface andthe second pressure impingement surface being substantially equal; aconstriction of the valve slide via which a pressure difference betweenan opening pressure and a closing pressure can be generated; and atleast one channel that connects an interior space of the valve slide toan exterior space of the valve slide.
 18. The valve according to claim17, further comprising a force accumulator configured to preload thevalve slide.
 19. The valve according to claim 17, wherein the at leastone channel connects the interior space of the valve slide to an annularspace around the valve slide configured to accommodate a spring.
 20. Thevalve according to claim 17, wherein the at least one channel isarranged in a region of the constriction.
 21. The valve according toclaim 17, wherein the constriction is formed as circular cross-sectionalnarrowing.
 22. The valve according to claim 17, further comprisingwherein a circumferential projection of the valve slide at the inputside that guides the valve slide in the valve housing and limits anannular space around the valve slide.
 23. The valve according to claim17, wherein walls of the valve slide on the output side have at leastone recess.
 24. The valve according to claim 23, wherein the valve slidehas at least two symmetrically arranged recesses.
 25. The valveaccording to claim 17, wherein the at least one flow path is a main flowpath that can be closed by the valve slide and is fluidically connectedas flow path to the output side of the valve.
 26. The valve according toclaim 17, wherein the at least one flow path is a bypass path that canbe closed by the valve slide and is fluidically connected as a flow pathto the input side of the valve.
 27. The valve according to claim 26,further comprising a pressure limiting valve arranged in the bypasspath.
 28. The valve according to claim 27, wherein the pressure limitingvalve is a check valve preloaded in closing direction.
 29. A vibrationdamper for a motor vehicle, comprising: a valve comprising: a valvehousing; an input side of the valve; an output side of the valve; avalve slide movable in the valve housing configured to at leastpartially close at least one flow path of a fluid flowing through thevalve; a first pressure impingement surface of the valve slide for anopening pressure; a second pressure impingement surface of the valveslide for a closing pressure, the first pressure impingement surface andthe second pressure impingement surface being substantially equal; aconstriction of the valve slide via which a pressure difference betweenan opening pressure and a closing pressure can be generated; and atleast one channel that connects an interior space of the valve slide toan exterior space of the valve slide.
 30. The vibration damper accordingto claim 29, further comprising: three tube elements arranged one insidethe other; and a displaceable piston arranged in an inner tube element,wherein: the valve is arranged at or inside the inner tube element, acenter tube element separates a main flow path from a bypass path, andthe main flow path and the bypass path are fluidically connected to theinterior of the inner tube element.
 31. The vibration damper accordingto claim 30, wherein a damping force generating device is arranged inthe main flow path.
 32. A motor vehicle comprising a vibration dampercomprising: a valve comprising: a valve housing; an input side of thevalve; an output side of the valve; a valve slide movable in the valvehousing configured to at least partially close at least one flow path ofa fluid flowing through the valve; a first pressure impingement surfaceof the valve slide for an opening pressure; a second pressureimpingement surface of the valve slide for a closing pressure, the firstpressure impingement surface and the second pressure impingement surfacebeing substantially equal; a constriction of the valve slide via which apressure difference between an opening pressure and a closing pressurecan be generated; and at least one channel that connects an interiorspace of the valve slide to an exterior space of the valve slide. 33.The valve according to claim 18, wherein the force accumulator is aspring.